Astronauts Chris Cassidy and Tom Marshburn ventured into space May 11, 2013, and replaced a pump unit on the outside of the International Space Station that was leaking ammonia. // NASA

Over the weekend, the crew of the International Space Station worked overtime to fix a leaking cooling network outside the orbital outpost. Astronauts Chris Cassidy and Tom Marshburn ventured into space on Saturday and replaced a pump unit that was leaking ammonia.

After more than five hours working outside, the astronauts seem to have solved the problem. Liquid ammonia is used to keep the space station at the right temperature by being pumped through external radiators to lose excess heat.

The spacewalk was the last major job for the crew, who will return to Earth tonight in a Soyuz spacecraft. That team, including Canadian astronaut and commander Chris Hadfield, handed over command on Sunday.

The station will operate with the three remaining crew members until the next Soyuz arrives May 29 with the European Space Agency’s (ESA) astronaut Luca Parmitano, NASA astronaut Karen Nyberg, and cosmonaut Fyodor Yurchikhin. They will spend six months on the station conducting scientific experiments.

Luca has two spacewalks of his own planned to install new equipment and maintain the station. As Expedition 36/37 flight engineer, he will work on maintenance outside the station, replace a camera mounted on Japan’s Kibo module, and retrieve some experiments. One of his spacewalks will prepare for the arrival later this year of Russia’s Multipurpose Laboratory Module and the ESA-built European Robotic Arm.